318 



PROTOTRACHEATA. 



FIG. 170. VENTRAL VIEW OF THE 

 HEAD OF AN EMBRYO OF PERIPATUS CA- 

 PENSIS AT A LATE STAGE OF DEVELOPMENT. 



I. thickening of epiblast of procepha- 

 lic lobe to form supra-cesopkageal gan- 

 glion; m. process from procephalic lobe 

 growing over the first post-oral appen- 

 dage; o. mouth; e. eye; 1 and 2, first 

 and second pair of post-oral appendages. 



adult, that they are not true appendages. The next pair therefore 

 to the antennae is the first post-oral pair. It is the only pair con- 

 nected with the mouth. At their 

 extremities there is formed a pair of 

 claws similar to those of the ambu- 

 latory legs (fig. 171). The next and 

 largest pair of appendages in the 

 embryo are the oral papillaB. They 

 are chiefly remarkable for contain- 

 ing the ducts of the slime glands 

 which open at their bases. They 

 are without claws. The succeeding 

 appendages become eventually im- 

 perfectly five-jointed; two claws are 

 formed as cuticular investments of 

 papilla? in pockets of the skin at 

 the ends of their terminal joints. 



I have been able to make a few 

 observations on the internal structure 

 of the embryos from specimens sup- 

 plied to me by Moseley. These are so 

 far confined to a few stages, one slightly earlier, the others slightly later, 

 than the embryo represented in fig. 168 B. The epiblast is formed of a 

 layer of columnar cells, two deep on the ventral surface, except along the 

 median line where there is a well-marked groove and the epiblast is much 

 thinner (fig. 172). 



The nervous system of the 

 trunk is formed as two indepen- 

 dent epiblastic cords. In my 

 earlier stage these are barely se- 

 parated from the epiblast, but in 

 the later ones are quite indepen- 

 dent (fig. 172, v.n), and partly 

 surrounded by mesoblast. 



The supra-cesophageal ganglia 

 are formed as thickenings of the 

 epiblast of the ventral side of the 

 procephalic lobes in front of the 



stomodaBum. They are shewn at 

 FIG. 171. HEAD OF AN EMBRYO PERIPATUS. / /. n^ A rm.xi.-i r 



(From Moseley.) l m % l ' - The thickenings of 



The figure shews the jaws (mandibles), and tlie * wo sld A es are at first inde - 

 close to them epiblastic involutions, which pendent. At a somewhat later 

 grow into the supra-cesophageal ganglia. The period an invagination of the 

 antenna;, oral cavity, and oral papilla; are also epiblast grows into each of these 

 shewn> lobes. The openings of these in- 



vaginations extend from the oral cavity forwards ; and they are shown in 

 fig. 171 \ Their openings become closed, and the walls of the invaginations 

 constitute a large part of the embryonic supra-cesophageal ganglia. 



1 This figure is taken from Moseley. The epiblastic invaginations are represented 

 in it very accurately, and though not mentioned in the text of the paper, Moseley 



